Intervertebral spacers are devices that are well known for placing between two adjacent vertebrae in order to secure the two vertebrae to each other so as to maintain a fixed gap between them. French patent application FR 01/03362 in the name of the Applicant describes such spacers. It suffices to recall that the spacer is provided at each of its ends with a notch in which the spinous process of a vertebra is engaged. A system of ties or braids serves to secure each end of the spacer with the spinous process.
Nevertheless, putting such a spacer into place raises certain problems associated with the practice of surgery. There is a ligament known as the supraspinous ligament that interconnects the tips of all the spinous processes. In order to put the spacer into place, it is necessary to move that ligament. In practice, it is detached from the two spinous processes concerned, and it is moved away by means of a suitable surgical instrument. To detach the ligament from the spinous processes, a scalpel is used. Once the spacer has been put into place, the ligament is sewn back onto the spinous processes after making a small opening therein to receive the suture.
The major drawback of that surgical technique is that by acting on the ligament in order to detach it and then move it out of the way, it is weakened mechanically. In addition, all of those actions take time, which lengthens the duration of the surgery.
To remedy that drawback, proposals have already been made for intervertebral spacers that are made up of from two distinct portions. Each portion of the spacer is put into place on either side of the supraspinous ligament, and then by using appropriate surgical instruments, the two portions of the spacer are joined together. Such two-portion spacers are described in particular in U.S. Pat. No. 6,156,038. Nevertheless, the two-portion spacers described in that document are relatively difficult to use. In particular, assembling the two portions of the spacer together in situ is relatively difficult and it is not certain that the two parts will together form the spacer in suitable manner.